The present invention relates to a system for remotely controlling electrical appliances, and more particularly, to a system for remotely controlling electrical appliances utilizing power line communications and a data communication method therefor.
Power line communications have been utilized primarily to remotely control multiple electrical devices in distributed arrangements. In a typical power line communication system, data is modulated in a carrier having a frequency sufficiently higher than that of the AC supply voltage. The modulated wave packets are superimposed near zero-crossing points of the AC supply voltage so as to reduce an influence of noise in the power line on the system. Also, in order to further enhance a noise-immunity of the system, a data bit to be transmitted is represented by two packet positions as shown in FIG. 1. That is, a data bit is indicated by an existence or not of a packet at a zero-crossing point along with its complement at a next zero-crossing point.
In most applications utilizing such a power line communication method, more than two controllers are arranged in a manner that each controller is connected to an appliance. In such a system, however, if two controller attempts to transmit data simultaneously, data from the controllers collide and cannot be retrieved in a receiving party. Referring to FIG. 3, which illustrates a collision during a data transmission, two identical states may exist at neighboring zero-crossing points even though such a state is prohibited in a normal state.
Because of the reason, conventional power line communication methods have been not used for bidirectional communications. Also, any technical proposal for enabling bidirectional communications in a power line system has not been reported yet. Accordingly, in a conventional system, each of a plurality of receivers has to unilaterally receive control data from a master controller as shown in FIG. 2, but cannot send data to the master controller or another receiver. Even though such a system may be satisfactory in industrial applications such as a security alarm system, a garage door opener, and a lighting system in a building, the system cannot fulfill the needs of users at home. For example, a user at home wishes to control electrical appliances in each room no matter where she or he is.
To solve the above problem, one object of the present invention is to provide a system in which each controller allocated for each of a plurality of appliances communicates with one another so that the operation of the plurality of electric appliances in distributed arrangements are controlled conveniently.
Another object of the present invention is to provide a method for enabling bidirectional communications in a system utilizing power line communications, so that each controller engaged in the power line communication system communicates with each other.
To achieve one of the above objects, a control system of the present invention comprises: a power line; a plurality of controllers each of which is connected between the power line and one of the plurality of electric appliances; and input means for providing a control message to at least one of the plurality of controllers. The at least one of the plurality of controllers which receives the control message provides the control message to another one of the plurality of controllers via the power line. The at least one of the plurality of controllers which receives the control message may be selected arbitrarily by a user of the input means.
A method of transmitting data to the plurality of external controllers according to the present invention to achieve another one of the above objects is implemented in a controller connected to at least one electric appliance for controlling an operation of the at least one electric appliance and to a plurality of external controllers through a power line to communicate bidirectionally with the plurality of external controllers for receiving and transmitting a control message for controlling the operation of correspondingly connected electric appliance. The method comprises the steps of: (a) transmitting a first data to the plurality of external controllers via the power line and detecting a second data from the power line; (b) comparing the first and the second data; and in case that the first and the second data is not the same as each other, determining that a failure occurred, canceling the transmitting step, and re-transmitting the first data to the plurality of external controllers after a delay time is elapsed.